The Athenaeum or Melbourne Athenaeum is one of the oldest public institutions in Victoria, Australia, founded in 1839. The first President was Captain William Lonsdale, the first Patron was the Superintendent of Port Philip, Charles La Trobe and the first books were donated by Vice-President Henry Fyshe Gisborne. Originally it was called the Melbourne Mechanics' Institute. This was expanded in 1846 to the Melbourne Mechanics' Institution and School of Arts. The building on Collins Street was completed in 1842. The Athenaeum played a role in the establishment of Mechanics' Institutes in Victoria.

The Melbourne City Council met in the building until 1852 when the Melbourne Town Hall was built.

The Institution changed its name to the Melbourne Athenaeum in 1873. At that time, as now, a major activity was a library. In 1877, membership was 1681 and in 1879 there were 30,000 visits to the library. In 1880 it was reported 'that the floor of the large hall was the only one in Melbourne expressly constructed for dancing'. The front of the building was rebuilt in 1885 and 1886.

In October, 1896, the first movie was shown in Australia in the Athanaeum Hall. The Hall became a regular venue for screening films and the premier of The Story of the Kelly Gang by the Tait brothers was at the Athenaeum in 1906. The theatre in its present form was created in 1921. The theatre was the first venue in Australia to screen talking pictures. The Melbourne Theatre Company leased the theatre from 1976 to 1985 when the lease was taken over by various entrepreneurs who formed AT Management in 1997.

The Athenaeum housed a small museum in its early days and then an Art Gallery, which closed in 1971, after which it was converted into a smaller theatre space by the MTC. This space, as of 1997 is now home to the Comedy Club and, in the last few years, Melbourne Opera.

The library continues to exist as a large subscription library with members throughout Victoria, although its membership has declined from a peak of 7,579 in 1950.

The building was added to the Register of Historic Buildings in 1981 and is listed on the Victorian Heritage Register.

It has been used as a venue for the Melbourne International Comedy Festival and since 2006 has been the venue for the Last Laugh Comedy Club since it moved from North Melbourne.